High-side energy delivery through a single-quadrant thyristor triggered with a current-limiting switch

ABSTRACT

A cardiac rhythm management system includes an implantable cardiac rhythm management device that includes a defibrillation energy delivery circuit. The defibrillation energy delivery circuit provides high side energy delivery through a single-quadrant thyristor switch that is triggered by a current-limiting transistor switch. The defibrillation energy delivery circuit requires fewer electronic components, reducing the size and/or cost of the implantable cardiac rhythm management device. For example, the single-quadrant thyristor, designed to conduct and latch in only one quadrant (e.g., quadrant III) and having appropriate dV/dt and voltage blocking capabilities, may eliminate the need for additional series-coupled semiconductor devices. In another example, current-limiting is designed into, or inherent in, the semiconductor device triggering the single-quadrant thyristor, thereby eliminating the need for additional current-limiting circuits.

TECHNICAL FIELD

[0001] The present system relates generally to a system delivering highvoltage energy, and particularly, but not by way of limitation, to acardiac rhythm management system including a defibrillation energydelivery circuit having a high-side energy delivery through asingle-quadrant thyristor triggered with a current-limiting switch.

BACKGROUND

[0002] When functioning properly, the human heart maintains its ownintrinsic rhythm, and is capable of pumping adequate blood throughoutthe body's circulatory system. However, some people have irregularcardiac rhythms, referred to as cardiac arrhythmias. Such arrhythmiasresult in diminished blood circulation. One mode of treating cardiacarrhythmias uses drug therapy. Anti-arrhythmic drugs are often effectiveat restoring normal heart rhythms. However, drug therapy is not alwayseffective for treating arrhythmias of certain patients. For suchpatients, an alternative mode of treatment is needed. One suchalternative mode of treatment includes the use of a cardiac rhythmmanagement system. Portions of such systems are often implanted in thepatient and deliver therapy to the heart.

[0003] Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via an intravascular leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

[0004] Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering an high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock (“shock”). The shock interrupts the tachyarrhythmia,allowing the heart to reestablish a normal rhythm for the efficientpumping of blood. In addition to pacers, cardiac rhythm managementsystems also include, among other things, pacer/defibrillators thatcombine the functions of pacers and defibrillators, drug deliverydevices, and any other implantable or external systems or devices fordiagnosing or treating cardiac arrhythmias.

[0005] One problem faced by cardiac rhythm management systems is indelivering the high energy defibrillation shock. In one example, atransformer-coupled dc-to-dc voltage converter transforms a batteryvoltage (e.g., battery voltages approximately between 1.5 Volts and 6.5Volts) up to a high defibrillation voltage (e.g., defibrillationvoltages up to approximately 1000 Volts). The energy associated withthis high defibrillation voltage is typically stored on a storagecapacitor. A defibrillation energy delivery circuit delivers thedefibrillation energy from the storage capacitor to defibrillationleadwires and defibrillation electrodes associated with the heart. Uponreceiving this defibrillation energy via the defibrillation electrodes,the heart resumes normal rhythms if the defibrillation therapy issuccessful.

[0006] The defibrillation energy delivery circuit typically includesnumerous discrete electronic components that must be capable ofwithstanding the large voltages associated with the defibrillationenergy being delivered. These numerous discrete electronic components inthe defibrillation energy delivery circuit occupy considerable space inthe implantable cardiac rhythm management device. In order to improvepatient comfort and aesthetics, however, the implantable cardiac rhythmmanagement device should be small sized. Thus, a need exists for, amongother things, reducing the size and/or cost of the defibrillation energydelivery circuit.

SUMMARY OF THE INVENTION

[0007] This document describes, among other things, portions of acardiac rhythm management system including an implantable cardiac rhythmmanagement device that includes a defibrillation energy deliverycircuit. The defibrillation energy delivery circuit provides high sideenergy delivery through a single-quadrant thyristor switch that istriggered by a current-limiting transistor switch. The defibrillationenergy delivery circuit requires fewer electronic components, reducingthe number of assembly processing steps, cost and physical size of theimplantable cardiac rhythm management system. For example, thesingle-quadrant thyristor is designed for conduction/latching in asingle quadrant (e.g., quadrant III) and provides the necessary voltageblocking capabilities that can be used to eliminate the need foradditional series coupled voltage blocking semiconductor devices. Inanother example, current-limiting is designed into, or inherent in, thesemiconductor device triggering the single-quadrant thyristor, therebyeliminating the need for additional current-limiting circuits.

[0008] This document describes, among other things, a cardiac rhythmmanagement system. In one embodiment, the cardiac rhythm managementsystem includes a cardiac rhythm management device. The cardiac rhythmmanagement device includes a defibrillation energy delivery circuit. Thedefibrillation energy delivery circuit includes a first input terminal,receiving a first power supply, and a first single-quadrant thyristor,coupled between the first input terminal and a first output terminal.

[0009] In another embodiment, the cardiac rhythm management systemincludes a defibrillation energy delivery circuit. The defibrillationenergy delivery circuit includes a first input terminal, receiving afirst power supply. The defibrillation energy delivery circuit alsoincludes a first switch, coupled between the first input terminal and afirst output terminal. The defibrillation energy delivery circuitfurther includes a first current-limiting field-effect transistor (FET),coupled to the gate terminal of the first switch and sinking atriggering current.

[0010] This document also describes, among other things, a method ofdelivering defibrillation energy. The method includes receiving an inputvoltage, triggering a thyristor enabling single-quadrantconduction/latching, and coupling the input voltage to an outputterminal using the enabled thyristor. These and other aspects of thepresent system and methods will become apparent upon reading thefollowing detailed description and viewing the accompanying drawingsthat form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic drawing illustrating generally oneembodiment of portions of a cardiac rhythm management system and anenvironment in which it is used.

[0012]FIG. 2 is a schematic drawing illustrating generally oneembodiment of a cardiac rhythm management device, which is coupled to aheart, and certain aspects of the device.

[0013]FIG. 3 is a schematic/block diagram illustrating generally oneconceptual embodiment of portions of a defibrillation therapy circuit.

[0014]FIG. 4A is a graph illustrating generally one embodiment of aportion of a current vs. voltage characteristic of a triac, with thefour quadrants labeled I, II, III, and IV.

[0015]FIG. 4B is a graph illustrating generally one embodiment of aportion of a current vs. voltage characteristic of a single-quadrantthyristor, with the four quadrants labeled I, II, III, and IV.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents. In this document, “and/or” refers to non-exclusive “or”(e.g., “A and/or B” includes each of “A but not B.” “B but not A,” and“A and B”).

[0017] The present methods and apparatus will be described inapplications involving implantable medical devices including, but notlimited to, implantable cardiac rhythm management systems such aspacemakers, cardioverter/defibrillators, pacer/defibrillators, andbiventricular or other multi-site coordination devices. However, it isunderstood that the present methods and apparatus may be employed inunimplanted devices, including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, biventricular orother multi-site coordination devices, monitors, programmers andrecorders.

[0018] General System Overview and Examples

[0019] This document describes, among other things, high-side energydelivery through a single-quadrant thyristor triggered with a currentlimiting switch. The present cardiac rhythm management (CRM) systemprovides, among other things, an implantable CRM device. The CRM deviceincludes a defibrillation energy delivery circuit capable of deliveringhigh energy using fewer electronic components. This allows a smallersized CRM device.

[0020]FIG. 1 is a generalized schematic diagram illustrating generally,by way of example, but not by way of limitation, one embodiment of aportion of a CRM system 100. Various embodiments of system 100 includeexternal or implantable pacer/defibrillators, cardioverters,defibrillators, any combination of the foregoing, or any other systemusing or maintaining cardiac rhythms.

[0021] In the embodiment of FIG. 1, CRM system 100 includes a CRM device105 coupled to heart 110 via one or more endocardial or epicardialleadwires, such a pacing leadwire or a defibrillation leadwire 115.Defibrillation leadwire 115 includes one or more defibrillationelectrodes, such as for delivering defibrillation countershock (“shock”)therapy via first defibrillation electrode 120A and/or seconddefibrillation electrode 120B. Defibrillation leadwire 115 may alsoinclude additional electrodes, such as for delivering pacing therapy viafirst pacing electrode 125A (e.g., a “tip” electrode) and/or secondpacing electrode 125B (e.g., a “ring” electrode). Defibrillationelectrodes 120A-B and pacing electrodes 125A-B are typically disposed inor near one or more chambers of heart 110.

[0022] In the embodiment of FIG. 1, defibrillation leadwire 115 includesmultiple conductors that are insulated from each other for providingindependent connections between each electrode and cardiac rhythmmanagement device 105. In one embodiment, the defibrillation leadwire issecured to heart 110, such as by a corkscrew, a barb, or similarmechanism at or near first pacing electrode 125A. In another embodiment,CRM device 105 includes a hermetically sealed casing, a portion of whichprovides a conductive electrode that operates in conjunction with atleast one of the electrodes disposed in heart 110 for delivering pacingpulses and/or defibrillation countershocks and/or sensing electricalheart activity signals.

[0023] In one embodiment, CRM system 100 includes a remote userinterface, such as programmer 150, which permits communication with CRMdevice 105 using telemetry wand 155 or other communication device.Programmer 150 provides information to a physician or other caregiver,such as using a graphical user interface on a screen display, orproviding data using a strip chart recorder, or by any other technique.Programmer 150 also receives user input, such as for programming and/orcontrolling the functionality of programmer 150 and/or CRM device 105.

[0024] Example Cardiac Rhythm Management Device

[0025]FIG. 2 is a schematic diagram illustrating generally, by way ofexample, but not by way of limitation, one embodiment of portions ofdevice 105, which is coupled to heart 110. Device 105 includes a powersource 200, heart signal sensing circuit(s) 205, defibrillation therapycircuit(s) 215, a controller 220, and a communication circuit 225 forcommunicating with programmer 150 via telemetry device 155.

[0026] The heart signal sensing circuits 205 are coupled by one or moreleads 115 to one or more electrodes associated with heart 110 forreceiving, sensing, and/or detecting electrical heart signals. Suchatrial and/or ventricular heart signals correspond to heartcontractions. Such heart signals include normal rhythms, and abnormalrhythms including tachyarrhythmias, such as fibrillation, and otheractivity. Atrial sensing circuit 205 provides one or more signals tocontroller 220, via node/bus 230, based on the received heart signals.

[0027] In one embodiment, defibrillation therapy circuit(s) 215 providecardioversion/defibrillation therapy, as appropriate, to the heartelectrodes 120A-B. Controller 220 controls the delivery ofdefibrillation therapy by defibrillation therapy circuit(s) 215 based onheart activity signals received by sensing circuit(s) 205. Controller220 may further control the delivery of pacing therapy such as by apacing therapy circuit (not shown) via pacing electrodes 125A-B.Controller 220 includes various modules, which are implemented either inhardware or as one or more sequences of steps carried out on amicroprocessor or other controller. Such modules may be conceptualizedseparately, but it is understood that the various modules of controller220 need not be separately embodied, but may be combined and/orotherwise implemented, such as in software/firmware.

[0028] In general terms, sensing circuit(s) 205 sense electrical signalsfrom heart tissue in contact with the catheter lead(s) 115 to whichsensing circuit(s) 205 are coupled. Sensing circuit(s) 205 and/orcontroller 220 process these sensed signals. Based on these sensedsignals, controller 220 issues control signals to therapy circuit 215,if necessary, for the delivery of electrical energy (e.g.,defibrillation pulses) to the appropriate electrodes of lead 115.Controller 220 may include a microprocessor or other controller forexecution of software and/or firmware instructions. The software ofcontroller 220 may be modified (e.g., by remote external programmer 150)to provide different parameters, modes, and/or functions for theimplantable device 105 or to adapt or improve performance of device 105.

[0029]FIG. 3 is a schematic/block diagram illustrating generally, by wayof example, but not by way of limitation, one conceptual embodiment ofportions of defibrillation therapy circuit 215. In this embodiment,defibrillation therapy circuit 215 includes a defibrillation energygenerator circuit 300 and a defibrillation energy delivery circuit 305.In one example, defibrillation energy generator 300 includes atransformer-coupled dc-to-dc voltage converter that transforms a voltageprovided by power source 200 (e.g., source voltages of approximatelybetween 1.5 Volts and 6.5 Volts) up to a high defibrillation voltage(e.g., defibrillation voltages up to approximately 1000 Volts) at node310. The energy associated with this high defibrillation voltage istypically stored on a defibrillation energy storage capacitor 315 untildelivered to heart 110 via defibrillation energy delivery circuit 305and defibrillation electrodes 120A-B. While the defibrillation voltagesof up to approximately 1000 Volts generally describes currentapplications, defibrillation voltages may often fall within the range ofapproximately 600 to 800 Volts, such as approximately 780 Volts orapproximately 645 Volts. Regardless, the various embodiments of theinvention are not limited by such defibrillation voltages and may beadapted to other voltages.

[0030] Defibrillation energy delivery circuit 305 includes a first inputterminal that receives a first power supply voltage (e.g., the voltageassociated with the defibrillation energy at node 310) and a secondinput terminal that receives a second power supply voltage (e.g., theground voltage at node 320). Energy delivery circuit 305 includes anH-bridge 325, which includes four switches (i.e., first and secondpull-up switches 330A-B and first and second pull-down switches 335A-B)for coupling the defibrillation energy at node 310 and the groundvoltage at node 320 to first and second output terminals at nodes340A-B, respectively. Nodes 340A-B are coupled to defibrillationelectrodes 120A-B, respectively.

[0031] Pull-up switches 330A-B couple the defibrillation energy at node310 to respective first and second output terminals at nodes 340A-B,respectively. Pull-down switches 335A-B couple the ground voltage atnode 320 to respective first and second output terminals at nodes340A-B, respectively. In one embodiment, for delivering a monophasicdefibrillation energy pulse, control circuit 345 (which canalternatively be conceptualized as part of controller 220) turns onpull-down switch 335A, then turns on pull-up switch 330B. To discontinueenergy delivery, control circuit 345 turns off pull-down switch 335A,thus turning off pull-up switch 330B. To further deliver a biphasicdefibrillation energy pulse, control circuit 345 then turns on pull-downswitch 335B, then turns on pull-up switch 330A. To discontinue energydelivery, control circuit 345 then turns off pull-down switch 335B, thusturning off pull-up switch 330A. Multiphasic energy delivery may begenerated by repeating the cycle of delivering and discontinuing anenergy pulse in similar fashion for three or more cycles. It is thusinherent that the two cycles of biphasic energy delivery are a subset ofthe three or more cycles of multiphasic energy delivery. In oneembodiment, the user can select between monophasic, biphasic ormultiphasic energy delivery using programmer 150 to program device 105to operate accordingly.

[0032] In one embodiment, by way of example, but not by way oflimitation, pull-down switches 335A-B include insulated gate bipolartransistors (IGBTs) or other switching devices that couple therespective first and second defibrillation electrodes 120A-B to groundnode 320. In one embodiment, first pull-down switch 335A includes acollector coupled to first defibrillation electrode 120A, a gate coupledto receive control signal S1 at node 350 from control circuit 345, andan emitter coupled to ground node 320. Second pull-down switch 335Bincludes a collector coupled to second defibrillation electrode 120B, agate coupled to receive control signal S2 at node 355 from controlcircuit 345, and an emitter coupled to ground node 320.

[0033] In one embodiment, by way of example, but not by way oflimitation, first and second pull-up switches 330A-B include triacs,thyristors, semiconductor-controlled rectifiers (SCRs),semiconductor-controlled switches (SCSs), four-layer diodes or otherswitching devices that couple the high voltage associated with thedefibrillation energy at node 310 to first and second defibrillationelectrodes 120A-B, respectively. In one embodiment, control signals S3and S4 are received at nodes 360 and 365, respectively, from controlcircuit 345 to initiate operation of first and second pull-up switches330A-B, respectively. In one embodiment, control signals S3 and S4activate triggering devices 370A-B, which provide triggering signals tothe gates of switches 330A-B, respectively.

[0034] In a further embodiment, first and second pull-up switches 330A-Binclude single-quadrant thyristors. A triac (also referred to as abilateral triode switch) typically latches into a conducting state inthree quadrants of the four quadrants in its current vs. voltage graph.FIG. 4A is a graph illustrating generally, by way of example, but not byway of limitation, one embodiment of a portion of a current vs. voltagecharacteristic of a triac, with the four quadrants labeled I, II, III,and IV. Each of quadrants I, II, and III include a resistive/blockingstate 405 (indicated by a portion of the curve running approximatelyparallel to the voltage axis) and a conductive/latching state 410(indicated by a portion of the curve running approximately parallel tothe current axis). An appropriate trigger current, I_(G), to the gate ofthe triac reduces the breakover voltage magnitude ν_(bo) between theresistive and conductive states, allowing the triac to latch into theconductive state. The solid lines generally depict breakover voltage ata trigger current of zero. The dashed lines generally depict the effecton breakover voltage at a trigger current of magnitude greater than zero(absolute value greater than zero for quadrant I and absolute value lessthan zero for quadrants II and III).

[0035] By contrast, FIG. 4B is a graph illustrating generally, by way ofexample, but not by way of limitation, one embodiment of a portion of acurrent vs. voltage characteristic of a single-quadrant thyristor. Onlythe third quadrant, quadrant III, includes both a resistive/blockingstate 405 and a conductive/latching state 410 within the range oftrigger currents as described herein. Quadrants I, II, and IV includeonly resistive/blocking states (although it is understood that quadrantII could have a conductive region, albeit without latching; this isimplied, but not shown in FIG. 4B). It is also understood thatsingle-quadrant thyristors for use with the various embodiments of theinvention could provide a conductive/latching state using quadrantsother than the exemplary third quadrant without departing from the scopeof the teachings of this document, provided only one quadrant of thesingle-quadrant thyristor includes both a resistive/blocking state andthe conductive/latching state as described herein.

[0036] The gate triggering current for which it is designed latches thesingle-quadrant thyristor in a conductive/latching state in essentiallyonly one quadrant of the current vs. voltage characteristic graph. It isunderstood that it may be possible to conduct through thesingle-quadrant thyristor in other quadrants as well, but that asubstantially larger gate triggering current, i.e., exceeding deviceratings, is required to initiate conduction in those other quadrants.Stated differently, triggering devices 370A-B are designed to sink atrigger current from the gates of switches 330A-B to enable and latchconduction from node 310 to one of respective nodes 340A-B in only asingle quadrant of the current vs. voltage graph. In one example, anegative trigger current to, or a current sink from, each of thesingle-quadrant thyristors 330A-B couples the large positive voltageassociated with the defibrillation energy at node 310 to a respectiveone of electrodes 120A-B.

[0037] Single-quadrant thyristors of the type used for the variousembodiments of the invention are also capable of withstanding rapiddV/dt transitions (e.g., 300 V/μs minimum). Rapid voltage versus timetransitions (dV/dt) during defibrillation energy delivery occur at nodes120A and/or 120B during turn-on and/or turn-off of pull-down switches335A and/or 335B. Because such single-quadrant thyristors are designedto 1) withstand such dV/dt transitions; 2) provide high voltage blockingcapabilities (e.g., 1200V minimum); and 3) conduct/latch in only onequadrant (e.g., quadrant III), additional semiconductor devices inseries with triac/thyristor devices may be eliminated. This eliminationof such series components in the defibrillation energy delivery circuit305 may reduce the number of processing steps, reduce cost and reducethe physical size of the implantable cardiac rhythm management device.

[0038]FIG. 3 also illustrates triggering devices 370A-B, as discussedabove. In one embodiment, triggering devices 370A-B includecurrent-limiting switches such as, for example, high voltage n-channelfield-effect transistors (FETs) that, when turned on by control signalsS3 and S4, function in their saturation region of operation. Unliketypical FET designs, which provide high drain-source current insaturation, the present triggering devices 370A-B of one embodiment aredesigned with an effective low transconductance, which provides arelatively low drain-source current in saturation.

[0039] In one embodiment, this effective low transconductance isobtained by enabling for conduction a preselected number of availableparallel conducting channels in triggering devices 370A-B to obtain thedesired transconductance. In one example, triggering devices 370A-B arepower metal-oxide-semiconductor FETs (MOSFETs) with vertically orientedconducting channels. A gate and source are associated with a first sideof the semiconductor substrate of triggering devices 370A-B, and a drainis associated with an opposing second side of the semiconductorsubstrate of triggering devices 370A-B. A vertical channel is formedthrough the substrate between source and drain under control by thegate. By fabricating the power MOSFET with a plurality ofdrain-to-source channels, a plurality of vertical conducting channelsbecome available. By selecting a predetermined number of the verticalchannels for activation by the associated gate, a desiredtransconductance can be obtained.

[0040] The desired transconductance is achieved, based on the turn-ongate voltage (e.g., approximately between 10 Volts and 12 Volts)provided by control circuit 345, to provide the desired trigger currentto latch the single-quadrant thyristor switches 330A-B into a conductingand latched state. In one embodiment, the first and secondcurrent-limiting switch triggering devices 370A-B each sink triggeringcurrents from the respective first and second single-quadrant thyristorswitches 330A-B of approximately between 100 and 235 milliamperes,inclusive, such that thyristor switches 330A-B latch into theirconductive states. As an example, a single-quadrant thyristor switch mayhave a nominal triggering current of approximately 80 milliamperesrequired to latch into its conductive state. Its associated triggeringdevice may be specified to have an engineering margin such that thetriggering device produces a triggering current in excess of the nominalvalue, e.g., the triggering device may sink triggering currents ofapproximately 100 milliamperes in this example. In one particularembodiment, each of current-limiting FET switches 370A-B provides anon-state forward transconductance of less than or equal to approximately45 milliSiemens. In any case, the first and second current-limitingswitch triggering devices 370A and 370B are selected to achievesufficient current sink at a given gate drive to trigger theirrespective thyristor switch 330A and 330B, respectively.

[0041] In FIG. 3, current-limiting FETs 370A-B are modeled asgain-degenerated devices that include respective source-degenerationresistors 375A-B. It is understood, however, that in one embodiment,source-degeneration resistors 375A-B do not represent resistors separateand distinct from devices 370A-B, but merely represent the on-stateintegrated source resistance associated with each of current-limitingFETs 370A-B. The on-state source resistance and/or forwardtransconductance is selected by enabling a predetermined number ofavailable parallel conducting channels, as discussed above. By usingtriggering devices 370A-B that are inherently current-limiting, the needfor additional circuits to perform such current-limiting functions isavoided. This reduces the number of electronic components required forenergy delivery circuit 305, which may further reduce the number ofassembly processing steps, reduce cost and reduce the physical size ofthe implantable cardiac rhythm management device.

[0042] In one embodiment, defibrillation energy delivery circuit 305also includes additional electronic components, such as for determiningdefibrillation lead impedance. One example of using such additionalelectronic components for determining defibrillation lead impedance isdescribed in U.S. patent application Ser. No. 09/236,911 to Linder etal., filed Jan. 25, 1999, which is commonly assigned and incorporatedherein by reference.

Conclusion

[0043] This document describes, among other things, portions of acardiac rhythm management system including an implantable cardiac rhythmmanagement device that includes a defibrillation energy deliverycircuit. The defibrillation energy delivery circuit provides high sideenergy delivery through a single-quadrant thyristor switch that istriggered by a current-limiting transistor switch. The defibrillationenergy delivery circuit requires fewer electronic components, reducingthe size and/or cost of the implantable cardiac rhythm managementdevice. For example, the single-quadrant thyristor, designed to conductand latch in only one quadrant (e.g., quadrant III) and havingappropriate dV/dt and voltage blocking capabilities, may eliminate theneed for additional series-coupled semiconductor devices. In anotherexample, current-limiting is designed into, or inherent in, thesemiconductor device triggering the single-quadrant thyristor, therebyeliminating the need for additional current-limiting circuits.

[0044] It is to be understood that the above description is intended tobe illustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. For example, while the various embodiments referred tospecific values of voltages, transconductance, triggering currents,etc., such values are at the discretion of the designer and couldinclude values outside the range of the specific examples given. Thescope of the invention should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

What is claimed is:
 1. A cardiac rhythm management system, the systemincluding: a cardiac rhythm management device, the device including adefibrillation energy delivery circuit, the defibrillation energydelivery circuit including: a first input terminal, receiving a firstpower supply; and a first single-quadrant thyristor, coupled between thefirst input terminal and a first output terminal.
 2. The system of claim1, further including: a second single-quadrant thyristor, coupledbetween the first input terminal and a second output terminal; gateterminals associated with the first and second thyristors; a firstswitch, coupled to the gate terminal of the first thyristor for sinkinga triggering current; and a second switch, coupled to the gate terminalof the second thyristor for sinking a triggering current.
 3. The systemof claim 2, in which the first and second switches include field-effecttransistors (FETs).
 4. The system of claim 3, in which the first andsecond switches include current-limiting FETs.
 5. The system of claim 4,in which the first and second switches include a plurality of availableconducting channels, of which a preselected number of the conductingchannels are enabled for conduction.
 6. The system of claim 4, in whichthe first and second switches sink triggering currents from therespective first and second thyristors sufficient to enable and latchconduction of the respective first and second thyristors.
 7. The systemof claim 4, in which the first and second switches provide an on-stateforward transconductance of less than or equal to approximately 45milliSiemens.
 8. The system of claim 1, in which the first and secondthyristors are directly connected to the first and second outputterminals, respectively.
 9. The system of claim 8, in which the firstinput signal receives the first power supply voltage magnitude of up toapproximately 1000 Volts.
 10. The system of claim 9, in which the firstinput signal receives the first power supply voltage magnitude withinthe range of approximately 600 to 800 Volts.
 11. The system of claim 1,in which the first and second single-quadrant thyristors are configuredfor conduction/latching in a third quadrant only.
 12. A cardiac rhythmmanagement system, the system including: a cardiac rhythm managementdevice, the device including a defibrillation energy delivery circuit,the defibrillation energy delivery circuit including: a first inputterminal, receiving a first power supply; a first switch, coupledbetween the first input terminal and a first output terminal; and afirst current-limiting field-effect transistor (FET), coupled to thegate terminal of the first switch and sinking a triggering current. 13.The system of claim 12, further including: a second switch, coupledbetween the first input terminal and a second output terminal; and asecond current-limiting FET, coupled to the gate terminal of the secondswitch and sinking a triggering current, and in which the first andsecond FETs include a plurality of available conducting channels, ofwhich a preselected number of the conducting channels are enabled forconduction.
 14. The system of claim 13, in which the first and secondFETs sink triggering currents from the respective first and secondswitches sufficient to enable and latch conduction of the first andsecond switches.
 15. The system of claim 14, in which the first andsecond FETs provide an on-state forward transconductance of less than orequal to approximately 45 milliSiemens.
 16. The system of claim 15, inwhich the first and second switches each include a single-quadrantthyristor configured for conduction/latching in a third quadrant.
 17. Acardiac rhythm management system, the system including: a cardiac rhythmmanagement device, the device including a defibrillation energy deliverycircuit, the defibrillation energy delivery circuit including: a firstinput terminal, receiving a first power supply; a first single-quadrantthyristor, coupled between the first input terminal and a first outputterminal, and in which the first thyristor is configured forconduction/latching in its third quadrant; a second single-quadrantthyristor, coupled between the first input terminal and a second outputterminal, and in which the second thyristor is configured forconduction/latching in its third quadrant; a first current-limitingswitch, coupled to the gate terminal of the first thyristor for sinkinga triggering current; and a second current-limiting switch, coupled tothe gate terminal of the second thyristor for sinking a triggeringcurrent.
 18. The system of claim 17, in which the defibrillation energydelivery circuit further includes: a second input terminal, receiving asecond power/ground supply; a first pull-down switch, coupled betweenthe second input terminal and the first output terminal; and a secondpull-down switch, coupled between the second input terminal and thesecond output terminal.
 19. The system of claim 18, in which the firstand second pull-down switches each include an insulated gate bipolartransistor (IGBT).
 20. The system of claim 19, in which the first andsecond current-limiting switches each include a field-effect transistor(FET).
 21. The system of claim 17, further including first and secondlead electrodes respectively coupled to the first and second outputterminals.
 22. A method of delivering defibrillation energy, the methodincluding: receiving an input voltage; triggering a thyristor enablingsingle-quadrant conduction/latching; and coupling the input voltage toan output terminal using the enabled thyristor.
 23. The method of claim22, in which triggering the thyristor includes latching third quadrantconduction.
 24. The method of claim 22, in which triggering thethyristor includes sinking a gate current from the thyristor.
 25. Themethod of claim 24, in which sinking a gate current from the thyristorincludes limiting the gate current to a predetermined approximate value.26. The method of claim 22, in which coupling the input voltage to theoutput terminal includes providing a monophasic energy pulse.
 27. Themethod of claim 22, in which coupling the input voltage to the outputterminal includes providing a biphasic energy pulse.
 28. The method ofclaim 22, further including: enabling a pull-down switch; and couplingthe output terminal to a ground voltage.
 29. The method of claim 28, inwhich enabling and coupling the pull-down switch are carried out beforetriggering the thyristor and coupling the input voltage.
 30. A method ofdelivering defibrillation energy, the method including: receiving adefibrillation energy; receiving a ground voltage; coupling the groundvoltage to a first output terminal; triggering a first thyristorenabling single-quadrant latching of conduction in its third quadrant;coupling the defibrillation energy to a second output terminal using theenabled first thyristor; decoupling the ground voltage from the firstoutput terminal; and decoupling the defibrillation energy from thesecond output terminal by disabling the first thyristor.
 31. The methodof claim 30, further including: coupling the ground voltage to thesecond output terminal; triggering a second thyristor enablingsingle-quadrant latching of conduction in its third quadrant; couplingthe defibrillation energy to the first output terminal using the enabledsecond thyristor; decoupling the ground voltage from the second outputterminal; and decoupling the defibrillation energy from the first outputterminal by disabling the second thyristor.
 32. The method of claim 31,in which triggering the second thyristor includes sinking a triggercurrent of a predetermined approximate magnitude from the secondthyristor.
 33. The method of claim 32, in which sinking a triggercurrent from the second thyristor includes: triggering the secondthyristor gate using a field-effect transistor (FET); andcurrent-limiting the FET by using a preselected number of availableconducting channels.
 34. The method of claim 30, in which triggering thefirst thyristor includes sinking a trigger current of a predeterminedapproximate magnitude from the first thyristor.
 35. The method of claim34, in which sinking a trigger current from the first thyristorincludes: triggering the first thyristor gate using a field-effecttransistor (FET); and current-limiting the FET by using a preselectednumber of available conducting channels.